1. Field of the Invention
The present invention relates to a piezoelectric material, more specifically, to a piezoelectric material that does not contain any lead component. Further, the present invention relates to a piezoelectric element, a multilayered piezoelectric element, a liquid discharge head, a liquid discharge apparatus, an ultrasonic motor, an optical device, a vibrating apparatus, a dust removing apparatus, an imaging apparatus, and an electronic device, in which the piezoelectric material is employed.
2. Description of the Related Art
Lead zirconate titanate is a representative lead-containing piezoelectric material, which can be used in various piezoelectric devices, such as an actuator, an oscillator, a sensor, and a filter. However, a lead component is harmful to the ecological system because there is a possibility that the lead component of a wasted piezoelectric material may dissolve into the soil. Accordingly, research and development enthusiastically performed recently is directed to non-lead piezoelectric materials that can realize non-lead piezoelectric devices.
When a piezoelectric element is employed in a home electrical appliance or a similar product, it is required that the piezoelectric performances do not greatly change in an operating temperature range of the product. If a parameter relating to the piezoelectric performances, e.g., an electromechanical coupling factor, a dielectric constant, a Young's modulus, a piezoelectric constant, a mechanical quality factor, or a resonance frequency, greatly changes (for example, by an amount equivalent to 30% or more) depending on the temperature, it becomes difficult to obtain stable element performances in the operating temperature range. In a phase transition of the piezoelectric material according to the temperature, the piezoelectricity is maximized at a phase transition temperature. Therefore, the phase transition is a factor that causes a great change in piezoelectric characteristics. Therefore, it is a key to obtain a product whose piezoelectric performances do not change so greatly in the operating temperature range that the phase transition temperature of a piezoelectric material is not in the operating temperature range.
When a resonance device (e.g., an ultrasonic motor) includes a piezoelectric composition, the mechanical quality factor that represents the sharpness of resonance is required to be large. If the mechanical quality factor is low, an amount of electric power required to operate a piezoelectric element becomes higher and a driving control of the piezoelectric element becomes difficult due to heat generation. This is the reason why a piezoelectric material possessing a higher mechanical quality factor is required.
A non-lead piezoelectric material expressed by a pseudo-binary system solid solution of {[(Ba1-x1M1x1)((Ti1-xZrx)1-y1N1y1)O3]-δ% [(Ba1-yCay)1-x2M2x2)(Ti1-y2N2y2)O3]}, in which M1, N1, M2, and N2 are additive chemical elements, is discussed in Japanese Patent Application Laid-Open No. 2009-215111. (Ba1-x1M1x1)((Ti1-xZrx)1-y1N1y1)O3 is a rhombohedral and (Ba1-yCay)1-x2M2x2) (Ti1-y2N2y2)O3 is a tetragonal. Dissolving two components different in the crystal system enables to adjust the temperature at which the phase transition occurs between the rhombohedral and the tetragonal around the room temperature. For example, according to the discussed contents, the phase transition of BaTi0.8Zr0.2O3-50% Ba0.7Ca0.3TiO3 occurs around the room temperature and a piezoelectric constant d33 at 20° C. is 584 pC/N. On the other hand, a piezoelectric constant d33 at 70° C. of the same material is 368 pC/N. More specifically, if an increased amount in the temperature is 50° C., a reduction amount in the piezoelectric constant d33 is 37%. The above-mentioned piezoelectric material is characterized in that a phase transition at which the piezoelectricity is maximized occurs around the room temperature. Therefore, although the above-mentioned piezoelectric material demonstrates excellent piezoelectric performances around the room temperature, it is not desired that the piezoelectric performances is remarkably variable depending on the temperature. In the above-mentioned material, the Zr amount (x) is set to be greater than 0.1 to obtain a rhombohedral of (Ba1-x1M1x1) ((Ti1-xZrx)1-y1N1y1)O3, which is an edge component.
The material discussed in Karaki, 15th US-Japan Seminar on Dielectric and Piezoelectric Ceramics Extended Abstract, p. 40 to 41 is a non-lead piezoelectric ceramics that can be obtained by sintering BaTiO3 that includes additives of MnO (0.03 parts by weight (parts by weight)) and LiBiO2 (0 to 0.3 parts by weight) according to a two-step sintering method. The addition of LiBiO2 substantially increases the coercive field of BaTiO3 including the additive of MnO (0.03 parts by weight) linearly in proportion to the addition amount of LiBiO2. Further, the addition of LiBiO2 substantially decreases the piezoelectric constant d33, the dielectric constant, and the dielectric tangent. When the addition amount of LiBiO2 is 0.17 parts by weight, the piezoelectric constant d33 is 243 pC/N and the coercive field is 0.3 kV/mm. When the addition amount of LiBiO2 is 0.3 parts by weight, the coercive field is 0.5 kV/mm. However, according to an evaluation result, the above-mentioned piezoelectric material is not desired in that the temperature at which a phase transition occurs between the tetragonal and the orthorhombic is in a range from 5° C. to −20° C. Further, the above-mentioned piezoelectric material is not desired in that the mechanical quality factor at the room temperature is low (less than 500).
The above-mentioned conventional non-lead piezoelectric ceramics is not desired in that the piezoelectric performances greatly vary in the operating temperature range of a piezoelectric element and the mechanical quality factor is small.
To solve the above-mentioned problems, the present invention is directed to a piezoelectric material that does not contain any lead component and is characterized in that the temperature dependency in the piezoelectric constant is small in the operating temperature range, the density is high, the mechanical quality factor is high, and the piezoelectric constant is satisfactory. Further, the present invention is directed to a piezoelectric element, a multilayered piezoelectric element, a liquid discharge head, a liquid discharge apparatus, an ultrasonic motor, an optical device, a vibrating apparatus, a dust removing apparatus, an imaging apparatus, and an electronic device, in which the piezoelectric material is employed.